You're using KDE so click the K(coglike) starter button, click Internet and
then click Kppp (all left mouse button).
What you do next will be obvious; if you haven't set up Kppp properly you
should get a series of set-up screens to fill.
You might like to left-click the Kppp icon from K>Panel>Add
Application>Internet>Kppp display to fix the telephone image onto the
panel at the bottom of the screen. Then you simply click it each time
you want to dial up.
HTH Ken Parkes.